Can't add hair to particle system
I can't see your baking settings in the video, but this behavior can be caused if your particles aren't baked, or if they are baked to a Disk Cache.
From the Manual:

Only Frames Baked to Memory are Editable!
If you cannot edit the particles, check that you are not baking to a Disk Cache.

To change this, uncheck &quot;Disk Cache&quot; in your cache settings.